refactor: convert to bun-workspaces monorepo (desktop/ + www/)

- Move the Tauri app (React frontend + Rust backend) into desktop/ via
  git mv — configs unchanged (relative paths: tauri.conf.json, vite.config.ts)
- Root package.json becomes a private bun workspace container with
  orchestration scripts; desktop package renamed gridline-desktop
- Scaffold www/ with Astro 7 + Tailwind v4 (hand-wired vite plugin,
  static output, ready for Dokploy)
- Update release.yml for the new layout: projectPath: desktop,
  desktop/src-tauri resource paths, rust-cache workspace path
- Update README + AGENTS.md structure trees and dev commands
- Verified: vitest (1074), cargo test (354), desktop build, tauri dev
  (window launches), tauri build (dmg + app bundles), Astro build

desktop/src-tauri/src/models/ssh.rs

@@ -0,0 +1,39 @@
+use serde::{Deserialize, Serialize};
+
+/// SSH tunnel configuration.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SshConfig {
+    pub host: String,
+    pub port: u16,
+    pub user: String,
+    /// "password" or "key"
+    pub auth_method: String,
+    pub password: Option<String>,
+    pub private_key_path: Option<String>,
+    pub passphrase: Option<String>,
+}
+
+impl SshConfig {
+    /// Create a new `SshConfig` with the required fields.
+    pub fn new(host: String, port: u16, user: String, auth_method: String) -> Self {
+        SshConfig {
+            host,
+            port,
+            user,
+            auth_method,
+            password: None,
+            private_key_path: None,
+            passphrase: None,
+        }
+    }
+
+    /// Validate SSH configuration.
+    ///
+    /// Returns `true` if:
+    /// - `host` is not empty
+    /// - `port` is in range 1..=65535 (u16 guarantees <= 65535)
+    /// - `user` is not empty
+    pub fn is_valid(&self) -> bool {
+        !self.host.is_empty() && self.port >= 1 && !self.user.is_empty()
+    }
+}